--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/thread/windows/win_ce_semaphore.c	Thu Jan 20 18:04:05 2011 -0800
@@ -0,0 +1,228 @@
+/* win_ce_semaphore.c
+
+   Copyright (c) 1998, Johnson M. Hart
+   (with corrections 2001 by Rainer Loritz)
+   Permission is granted for any and all use providing that this
+   copyright is properly acknowledged.
+   There are no assurances of suitability for any use whatsoever.
+
+   WINDOWS CE: There is a collection of Windows CE functions to simulate
+   semaphores using only a mutex and an event. As Windows CE events cannot
+   be named, these simulated semaphores cannot be named either.
+
+   Implementation notes:
+   1. All required internal data structures are allocated on the process's heap.
+   2. Where appropriate, a new error code is returned (see the header
+      file), or, if the error is a Win32 error, that code is unchanged.
+   3. Notice the new handle type "SYNCHHANDLE" that has handles, counters,
+      and other information. This structure will grow as new objects are added
+      to this set; some members are specific to only one or two of the objects.
+   4. Mutexes are used for critical sections. These could be replaced with
+      CRITICAL_SECTION objects but then this would give up the time out
+      capability.
+   5. The implementation shows several interesting aspects of synchronization, some
+      of which are specific to Win32 and some of which are general. These are pointed
+      out in the comments as appropriate.
+   6. The wait function emulates WaitForSingleObject only. An emulation of
+      WaitForMultipleObjects is much harder to implement outside the kernel,
+      and it is not clear how to handle a mixture of WCE semaphores and normal
+      events and mutexes. */
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#include "win_ce_semaphore.h"
+
+static SYNCHHANDLE CleanUp(SYNCHHANDLE hSynch, DWORD Flags);
+
+SYNCHHANDLE
+CreateSemaphoreCE(LPSECURITY_ATTRIBUTES lpSemaphoreAttributes,  /* pointer to security attributes */
+                  LONG lInitialCount,   /* initial count */
+                  LONG lMaximumCount,   /* maximum count */
+                  LPCTSTR lpName)
+/* Semaphore for use with Windows CE that does not support them directly.
+   Requires a counter, a mutex to protect the counter, and an
+   autoreset event.
+
+   Here are the rules that must always hold between the autoreset event
+   and the mutex (any violation of these rules by the CE semaphore functions
+   will, in all likelihood, result in a defect):
+    1. No thread can set, pulse, or reset the event,
+       nor can it access any part of the SYNCHHANDLE structure,
+       without first gaining ownership of the mutex.
+       BUT, a thread can wait on the event without owning the mutex
+       (this is clearly necessary or else the event could never be set).
+    2. The event is in a signaled state if and only if the current semaphore
+       count ("CurCount") is greater than zero.
+    3. The semaphore count is always >= 0 and <= the maximum count */
+{
+    SYNCHHANDLE hSynch = NULL, result = NULL;
+
+    __try {
+        if (lInitialCount > lMaximumCount || lMaximumCount < 0
+            || lInitialCount < 0) {
+            /* Bad parameters */
+            SetLastError(SYNCH_ERROR);
+            __leave;
+        }
+
+        hSynch =
+            HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, SYNCH_HANDLE_SIZE);
+        if (hSynch == NULL)
+            __leave;
+
+        hSynch->MaxCount = lMaximumCount;
+        hSynch->CurCount = lInitialCount;
+        hSynch->lpName = lpName;
+
+        hSynch->hMutex = CreateMutex(lpSemaphoreAttributes, FALSE, NULL);
+
+        WaitForSingleObject(hSynch->hMutex, INFINITE);
+        /*  Create the event. It is initially signaled if and only if the
+           initial count is > 0 */
+        hSynch->hEvent = CreateEvent(lpSemaphoreAttributes, FALSE,
+                                     lInitialCount > 0, NULL);
+        ReleaseMutex(hSynch->hMutex);
+        hSynch->hSemph = NULL;
+    }
+    __finally {
+        /* Return with the handle, or, if there was any error, return
+           a null after closing any open handles and freeing any allocated memory. */
+        result =
+            CleanUp(hSynch, 6 /* An event and a mutex, but no semaphore. */ );
+    }
+
+    return result;
+}
+
+BOOL
+ReleaseSemaphoreCE(SYNCHHANDLE hSemCE, LONG cReleaseCount,
+                   LPLONG lpPreviousCount)
+/* Windows CE equivalent to ReleaseSemaphore. */
+{
+    BOOL Result = TRUE;
+
+    /* Gain access to the object to assure that the release count
+       would not cause the total count to exceed the maximum. */
+
+    __try {
+        WaitForSingleObject(hSemCE->hMutex, INFINITE);
+        /* reply only if asked to */
+        if (lpPreviousCount != NULL)
+            *lpPreviousCount = hSemCE->CurCount;
+        if (hSemCE->CurCount + cReleaseCount > hSemCE->MaxCount
+            || cReleaseCount <= 0) {
+            SetLastError(SYNCH_ERROR);
+            Result = FALSE;
+            __leave;
+        }
+        hSemCE->CurCount += cReleaseCount;
+
+        /*  Set the autoreset event, releasing exactly one waiting thread, now or
+           in the future.  */
+
+        SetEvent(hSemCE->hEvent);
+    }
+    __finally {
+        ReleaseMutex(hSemCE->hMutex);
+    }
+
+    return Result;
+}
+
+DWORD
+WaitForSemaphoreCE(SYNCHHANDLE hSemCE, DWORD dwMilliseconds)
+   /* Windows CE semaphore equivalent of WaitForSingleObject. */
+{
+    DWORD WaitResult;
+
+    WaitResult = WaitForSingleObject(hSemCE->hMutex, dwMilliseconds);
+    if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0)
+        return WaitResult;
+    while (hSemCE->CurCount <= 0) {
+
+        /* The count is 0, and the thread must wait on the event (which, by
+           the rules, is currently reset) for semaphore resources to become
+           available. First, of course, the mutex must be released so that another
+           thread will be capable of setting the event. */
+
+        ReleaseMutex(hSemCE->hMutex);
+
+        /*  Wait for the event to be signaled, indicating a semaphore state change.
+           The event is autoreset and signaled with a SetEvent (not PulseEvent)
+           so exactly one waiting thread (whether or not there is currently
+           a waiting thread) is released as a result of the SetEvent. */
+
+        WaitResult = WaitForSingleObject(hSemCE->hEvent, dwMilliseconds);
+        if (WaitResult != WAIT_OBJECT_0)
+            return WaitResult;
+
+        /*  This is where the properties of setting of an autoreset event is critical
+           to assure that, even if the semaphore state changes between the
+           preceding Wait and the next, and even if NO threads are waiting
+           on the event at the time of the SetEvent, at least one thread
+           will be released. 
+           Pulsing a manual reset event would appear to work, but it would have
+           a defect which could appear if the semaphore state changed between
+           the two waits. */
+
+        WaitResult = WaitForSingleObject(hSemCE->hMutex, dwMilliseconds);
+        if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0)
+            return WaitResult;
+
+    }
+    /* The count is not zero and this thread owns the mutex.  */
+
+    hSemCE->CurCount--;
+    /* The event is now unsignaled, BUT, the semaphore count may not be
+       zero, in which case the event should be signaled again
+       before releasing the mutex. */
+
+    if (hSemCE->CurCount > 0)
+        SetEvent(hSemCE->hEvent);
+    ReleaseMutex(hSemCE->hMutex);
+    return WaitResult;
+}
+
+BOOL
+CloseSynchHandle(SYNCHHANDLE hSynch)
+/* Close a synchronization handle. 
+   Improvement: Test for a valid handle before dereferencing the handle. */
+{
+    BOOL Result = TRUE;
+    if (hSynch->hEvent != NULL)
+        Result = Result && CloseHandle(hSynch->hEvent);
+    if (hSynch->hMutex != NULL)
+        Result = Result && CloseHandle(hSynch->hMutex);
+    if (hSynch->hSemph != NULL)
+        Result = Result && CloseHandle(hSynch->hSemph);
+    HeapFree(GetProcessHeap(), 0, hSynch);
+    return (Result);
+}
+
+static SYNCHHANDLE
+CleanUp(SYNCHHANDLE hSynch, DWORD Flags)
+{                               /* Prepare to return from a create of a synchronization handle.
+                                   If there was any failure, free any allocated resources.
+                                   "Flags" indicates which Win32 objects are required in the 
+                                   synchronization handle. */
+
+    BOOL ok = TRUE;
+
+    if (hSynch == NULL)
+        return NULL;
+    if ((Flags & 4) == 1 && (hSynch->hEvent == NULL))
+        ok = FALSE;
+    if ((Flags & 2) == 1 && (hSynch->hMutex == NULL))
+        ok = FALSE;
+    if ((Flags & 1) == 1 && (hSynch->hEvent == NULL))
+        ok = FALSE;
+    if (!ok) {
+        CloseSynchHandle(hSynch);
+        return NULL;
+    }
+    /* Everything worked */
+    return hSynch;
+}
+
+/* vi: set ts=4 sw=4 expandtab: */